Booting into Safe Mode hangs

I've recently come home for the holidays to find that my parents' computer (Win2K with SP1) is so slow and problem-ridden that it's about to fall over. I know how to fix most of the problems, but when I tried I discovered that I can't even boot into Safe Mode!

When I try, I get to the "Starting Windows..." screen, the progress bar fills all the way up, then it hangs. It boots into normal mode fine (if rather slowly), and I'm at a loss about what could be causing this? I thought Safe Mode was supposed to be the reliable one!

Yep. I've scanned with Avast Anti-Virus, MS Anti-Spyware, Spybot Search and Destroy, Bazooka and Ad-Adware. All came up with nothing. I was trying to boot into Safe Mode to do another virus/spyware scan, and also to change a few other settings, but it doesn't want to load at all.

I've never had this problem before, and I'm quite anxious to get it fixed in case the machine starts to have major problems, and I need to use Safe Mode, but I can't find any reasons why this might be happening.

Thanks for the article, Robin0759. It described my problem exactly. MS didn't seem to have a solution though, but I went looking and found another article that suggested trying Last Known Good configuration. Unfortunately, at this point the machine collapsed entirely, so I'm doing a clean reinstall instead. Lucky the instructions were in this month's PCA!